Electron beam microcolumns based on microfabricated electron optical components and field emission sources operating under the scanning tunneling telescope (STM) aided alignment principle were first introduced in the late 1980s. Electron beam microcolumns are used to form a finely focused electron beam and offer the advantages of extremely high resolution with improved beam current, small physical size, and low cost, and can be used in a wide variety of applications, such as electron beam lithography. See "Electron-Beam Microcolumns for Lithography and Related Applications" by Chang, T. et al., Journal of Vacuum Science Technology Bulletin 14(6), pp. 3774-3781, November/December 1996, incorporated herein by reference.
The alignment principles used by microcolumns are similar to STMs in that a precision X-Y-Z positioner is used to control a sharp tip, in the case of a microcolumn a field emission tip, and to utilize the emission from the tip to measure the position of the tip. For additional information relating to three-axis micropositioners, see "Miniature Three-Axis Micropositioner for Scanning Proximal Probe and Other Applications," by S. Kleindiek et al., Journal of Vacuum Science Technology Bulletin 13(6), pp. 2653-2656, November/December 1995.
FIG. 1 is an exploded diagram of field emitter source 110 and electron optical column 120. Field emitter source 110 includes a field emitter tip 112, which may be a Zr/O/W Schottky field emitter tip or a cold-field emitter tip, such as a single crystal tungsten, hafnium carbide or diamond tip. Field emitter tip 112 is mounted on a miniature three-axis micropositioner 114. Micropositioner 114 has a range of movement in the order of tens of micrometers to more than 1 mm in each of the X-Y-Z directions and has subnanometer positioning capability. Micropositioner 114 is used to align field emitter tip 112 with electron optical column 120. Typical dimensions of miniature three-axis micropositioner 114 are approximately 2.times.2.times.1.1 cm.
The typical components of electron optical column 120 include a microsource lens 122 with an extractor 124 and an anode 128 with apertures of approximately a few micrometers and 100 .mu.m in diameter, respectively. Extraction electrode 124 is fabricated from 2 .mu.m thick silicon (Si) membrane with a bore diameter of a few microns. For optimum lens operation, emitter 112 is required to be positioned very closely and precisely aligned to extractor hole 126.
Due to the proximity of emitter source 110 to extractor 122, aligning emitter tip 112 to extractor hole 126 is difficult. The problem is exacerbated by the dimension of extractor electrode 124 and the overall column dimensions. For fine alignment, an STM-type X-Y positioner has been used in-situ to scan the tip over the extractor electrode. However, this approach requires time consuming scanning of relatively large areas.
Accordingly, it is clear that there is a need for a method to easily and precisely align an electron emitter and an extractor hole of a microcolumn.